Control system for furnace alternatively fired by gas and oil fuels



Aug. 14, 1956 I c. BERGTHOLDT ET AL 2,758,637

CONTROL SYSTEM FOR FURNACE ALTERNATIVELY FIRED BY GAS AND OIL. FUELS 2 Sheets-Sheet 1 Filed March 24, 1953 OIL BURNER 6H5 summer:

W Z c e5 m/ @m a Aug. 14, 1956 c, 'BERGTHQLDT ET AL 2,758,637

CONTROL SYSTEM FOR FURNACE ALTERNATIVEILY FIRED BY GAS AND OIL FUELS Filed March 24, 1953 2 Sheets-Sheet 2 SOLENOID OPERATED DIAPHRAM GA3 VALVE IGNITION ELECTRQDE LIMIT CONTROL SOLENOID OPERATED PILOT VALVE SOLENOlD OPERATED OIL BLOWER HOTO fff l, a 52 53 mmrnou ELEUEOIE gwuimfob United States Patent CONTROL SYSTEM FOR FURNACE ALTERNA- V TIVELY FIRED BY GAS AND OIL FUELS George C. Bergtholdt and Kurt S. Jaeger, Tulsa, Okla.., assignors to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application March 24, 1953, Serial No. 344,408

6 Claims. (Cl. 158-11) This invention relates to a control system for a furnace alternatively fired by oil or gaseous fuel, and, more particularly, to a control system that prevents the build up of carbonaceous material in an oil burner jet supplying oil fuel for combustion in a combustion chamber of such furnace.

In many areas gaseous fuels such as natural gas are appreciably less expensive than oil fuels, so that, from the cost standpoint, it is preferable to operate boilers, furnaces, and other heat-generating units on gaseous fuel. However, it is generally true that gas pressures in supply lines fluctuate substantially, and frequently, particularly during cold periods, are lower than the safe operating pressures for such gas burners. It has been suggested that furnaces, boilers, and other heat generating units be provided with gas burners to be fired when the gas pressure is sufiicient to make such firing satisfactory, and also be provided with oil burners to be fired when the gas pressure is too low. However, oil burner jets are provided with a plurality of minute openings through which the oil fuel is atomized into a combustion chamber, and in which some oil clings when such a jet is not firing. In all such furnaces heretofore suggested the oil film clinging in these openings when firing of the oil burner is discontinued is carbonized during firing of the gas burners. After at most a few cycles of firing oil and gas the carbonaceous deposit builds up to such an extent that the oil burner jet can no longer be fired and must be removed from the furnace, boiler, or other heating unit and thoroughly cleaned. After a few such cleaning operations it is likely that the jet will be completely unusable because of damage to the small openings therein caused by such cleaning.

The present invention is based upon the discovery of a control system for use in furnaces designed for alternative firing on gas and oil, which control system has been found in practice completely to avoid the build up of carbonaceous material in the oil burner jet, and, hence, the need for periodic removal and cleaning thereof.

It is, therefore, an object of the invention to provide a control system for furnaces, boilers, and other heating units designed for alternative gas and oil firing.

Other objects and advantages of the present invention will be apparent from the description which follows, and from the accompanying drawings, in which;

Fig. 1 is a schematic representation, in plan view, partially in cross-section, of a furnace or boiler constructed to be fired alternatively by oil fuel or by gaseous fuel;

Fig. 2 is a vertical sectional view along the line 2-2 of Fig. 1;

Fig. 3 is a view in perspective of a portion of the control system of the invention;

Fig. 4 is a view in vertical section generally along the plane represented by the lines 44 in Fig. 3; and

Fig. 5 is a wiring diagram showing the control circuits involved in the control system of the invention.

According to the invention an improved control system for a furnace having a combustion chamber, at least one gas burner jet extending into the chamber for supplying gaseous fuel for combustion therein, and an oil burner jet extending into the chamber for supplying oil fuel for combustion therein is provided. The improved control system consists in the combination of a shield surrounding the oil burner jet and extending into the chamber, a baffle for the end of said shield, means mounting the bafiie for movement between a first position shielding the open end of the shield, and a second position not obstructing the open end of the shield, means for moving the bafiie into the first position, means for moving the baflie into the second position, and means for preventing the firing of the oil burner except when the baflie is supported in the second position.

Referring now more particularly to the drawings, a furnace, boiler, or other heat generating unit having a combustion chamber 11, a shield 12 for an oil burner jet, and a housing 13 enclosing gas burners is represented schematically in Fig. l. A gas supply line 14, equipped with suitable regulating valves 15 and 16, is provided for supplying gaseous fuel for combustion by the gas burner jets. A pilot line 17 supplies gas for a pilot (not illustrated) through a solenoid operated pilot valve 18. An oil supply line 19 feeds oil fuel to a pump 20 driven by a blower motor 21. Oil is pumped from the pump 20 through a conduit 22, a solenoid controlled valve 23, and a tube 24 (Fig. 3) inside the shield 12 to an oil burner jet 25. The relative positions of the gas burner jets, which are positioned in tubes 26, and of the oil burner jet 25 can be seen in Fig. 2.

Mechanical details of the control system of the invention are shown in Figs. 3 and 4. The shield 12 surrounds the oil burner jet 25 and the tube 24, forming a housing excluding the tubes 26. A baffle 27 (see Fig. 3) is welded or otherwise rigidly attached to a shaft 28 journalled in bearings 29, welded or otherwise attached to a support- I ing frame member 30 which is rigidly attached as by a strap 31 to the shield 12. The baffle 27 is represented not obstructing an end 32 of the shield 12. The baflie 27 is swingable upon partial rotation of the shaft 28 in the direction of the arrow into a position obstructing the end 32 of the shield 12. In the specific embodiment of the invention illustrated, partial rotation of the shaft 28 is accomplished by limited vertical movement of a stalled motor 33 mounted on a plate 34 welded or otherwise rigidly attached to the frame member 30. the stalled motor 33 is transmitted to the shaft 23 (see. Fig. 4) through a lever 35 pinned at 36 to the plate 34, pinned at 37 to the drive shaft 38 of the stalled motor, and at 39 to a connecting rod 40. The connecting rod 40 is pinned to one end of an arm 41, the other end of which is welded or otherwise rigidly attached to the shaft 28. The vertical thrust of the drive shaft 38 of the stalled motor 33 is such that when the motor is energized the baffle 27 is raised to the position shown in Fig. 3, not obstructing the end 32 of the shield 12. When the stalled motor 33 is not energized'the drive shaft 38 moves down wardly a distance sufficient to permit the baffle 27 to drop into obstructing relationship with the end 32 of the shield 12. In the, specific embodiment of the invention illustrated, the bafile 27, when positioned in such obstructing relationship is spaced about 1 inch from the end 32 of the shield 12. An enabling switch schematically illustrated by contact 42 (Fig. 4) is activated by the lever 35 when the stalled motor 33 is energized, and a second enabling switch schematically illustrated by contact 43 is activated by the lever 35 when the stalled motor 33 is deenergized.

The essential features of a wiring diagram for operating the control system of the invention are shown in Fig. 5. A post 44 is attached to the energized side of an alter- Movement of nating current source, and a post 45 is connected to the ground side of such alternating current source. Current flows continuously from the post 44 through a primary coil 46 of a voltage reducing transformer. Current can also pass from the post through; a limit control 47 which is in the nature of a circuit breaker, and through an operating control 48 opened and closed by conventional control equipment (not illustrated). When the limit controls and the operating control are closed, as illustrated, current flows through them to a post 49, which constitutes a portion of the contacts 42 and 43, represented on the Wiring diagram as parts of a single pole double throw switch. The stalled motor 33 is represented in Fig. 5 as energized by a circuit connected to a secondary 50 forming, with the primary 46, a transformer, and with a single throw single pole switch 51 closed to complete the circuit. This is the position illustrated in Figs. 3 and 4 of the drawings. In this position current flows from the post 49 through the contact 42 and energizes the solenoid operated oil valve 23 permitting oil to flow through such valve, through the blower motor 21 to drive a blower (not illustrated) which supplies combustion air for the oil burner 25 and also operates the pump to provide oil for combustion to the burner 25, and to the primary coil of a transformer 52. The secondary coil of the transformer 52 is connected in closed circuit to an ignition electrode 53 which, in the diagram of Fig. 5, is illustrated as operating continuously.

When it is desired to change from oil fuel to gaseous fuel the single throw single pole switch 51 is opened, either manually, or automatically by control equipment (not illustrated), actuated, for example, by a sensing mechanism operated by the gas supply pressure. Opening the single throw single pole switch 51 de-energizes the stalled motor 33 and causes the shaft 38 to move vertically to the other limit of its travel. This movement of the shaft 38 (see Figs. 3 and 4), transmitted through the lever 35, the connecting rod 40, the arm 41, and the shaft 28, moves the baffle 27 into shielding or obstructing relationship with the end 32 of the shield 12, as discussed above. Movement of the lever 35 also'opens the. contact 42, and then closes the contact 43. When the contact 42 is opened, the solenoid operated oil valve 23, the blower motor 21 and the transformer 52 (Fig. 5) are de-energized.

When the contact 43 is closed current flows therefrom to a post 54, and thence through a normally closed pressure responsive switch 55 and the solenoid operated diaphragm gas valve 15, through a normally closed single throw single pole switch 56 to the primary of a transformer 57, and through the solenoid operated pilot valve 18. One side of the secondary coil of the transformer 57 is grounded, and the other is connected to one side'of an ignition electrode 58, the other side of which electrode is grounded.

In operation, when the gas burners are being fired the switch 51 is open and the shield 27 is in its shielding or obstructing relationship with the end 32 of the shield 12,

and protects the oil burner jet from radiant heat in the.

combustion chamber 11. Normal vacuum drawn in the combustion chamber 11 by the gas flame draws air continuously through the blower (not illustrated) which supplies combustion air to the oil burner, and around the shield and positively cools the burner. It has been found in practice that no carbonaceous deposit builds up on the burner 25 even after long repeated operation first on gas and then on oil, in the apparatus of the invention. When the single throw single pole switch 51 is closed, the contact 43 is opened before the baffle 27 is opened, and before the contact 42 is closed. As soon as the baffle 27 reaches a position not obstructing the end 32 of the shield 12, the contact 42 is closed and firing of oil begins. if the operating control 48 is closed.

Itwill be apparent that thev apparatus of the invention could be modified so that the contact 43 was closed as.

soon as the contact 42 was opened, if desired. Various other changes and modifications can be made in the apparatus illustrated and described without departing from the spirit of the claims, as the embodiments of the invention shown and described are intended as illustrative only.

Having described the invention, we claim:

1. In a furnace having a combustion chamber, at least one gas burner jet extending into the chamber for supplying gaseous fuel for combustion therein, a gas-cycle electrical control circuit for regulating the operation of the gas burner, an oil burner jet extending into the chamber for supplying oil fuel for combustion therein, and an oil-cycle electrical control circuit for regulating the operation of the oil burner, the improvement consisting in the combination of a shield surrounding the oil burner jet and having an open end extending into the chamber, a bafile for the end of said shield, means mounting said bafile for movement between a first position obstructing the open end of said shield and a second position not obstructing the open end of said shield, means for moving said baffle into such first position, means for moving said battle into such second position, gas switch means in the gas-cycle electrical control circuit having an open position breaking such circuit and a closed position enabling the energizing of such circuit, oil switch means in the oilcycle electrical control circuit having an open position breaking such circuit and a closed position enabling the energizing of such circuit, means to retain said gas switch means in such open position except when said bafile is in such first position, and means to retain said oil switch means in such open position except when said battle is in such second position.

2. In a furnace having a combustion chamber, at least one gas burner jet extending into the chamber for supplying gaseous fuel for combustion in the combustion chamber, a gas-cycle electrical control circuit for regulating the operation of the gas burner, an oil burner jet extending into the chamber for supplying oil fuel for combustion in the combustion chamber, and an oil-cycle electrical control circuit for regulating the operation of the oil burner, the improvement consisting in the combination of a shield surrounding the oil burner jet and having an open end extending into the chamber, a battle for the end of said shield, means mounting said bafiie for movement between a first position obstructing the open end of said shield and a second position not obstructing the open end of said shield, means for moving said bafiie into such first position, means for moving said battle into such second position, a single pole double throw enabling switch having a first position breaking the gas-cycle electrical control circuit and enabling the energizing of the oilcycle electrical control circuit, and a second position breaking the oil-cycle electrical control circuit and enabling the energizing of the gas-cycle electrical control circuit, and means to retain said single throw double pole switch in such second position except when said battle is in such second position.

3. In a furnace having a combustion chamber, at least one gas burner jet extending into the chamber for supplying gaseous fuel for combustion therein, a gas-cycle electrical control circuit for regulating the operation of the gas burner jet, an oil burner jet extending into the chamber for supplying oil fuel for combustion therein,

and an oil-cycle electrical control circuit for regulating.

the operation of the oil burner jet, the improvement consisting in the combination of a shield surrounding the oil burner jet and having an open end extending into the chamber, a baflie for the end of said shield, means mounting said battle for movement between a first position obstructing the open end of said shield and a second position not obstructing the open end of said shield, means for moving said bafile into such first position, means for moving said baffle into such second position, a single pole double throw enabling switch having a first position breaking the gas-cycle electrical control circuit and enabling the energizing of the oil-cycle electrical control circuit, a second position breaking the oil-cycle electrical control circuit and breaking the gas-cycle electrical control circuit, and a third position breaking the oil-cycle electrical control circuit and enabling the energizing of the gas-cycle electrical control circuit, means to retain said single throw double pole switch in such first position when said bafile is in such second position, means to retain said single throw double pole switch in such third position when said bafile is in said first position, and means to retain said single throw double pole switch in said second position when said bafile is intermediate between such first position and such second position.

4. In a furnace having a combustion chamber, at least one gas burner jet extending into the chamber for suplying gaseous fuel for combustion therein, a gas-cycle electrical control circuit for regulating the operation of the gas burner jet, an oil burner jet extending into the chamber for supplying oil fuel for combustion therein, and an oil-cycle electrical control circuit for regulating the operation of the oil burner jet, the improvement consisting in the combination of a shield surrounding the oil burner jet and having an open end extending into the chamber, a bafiie for the end of said shield, means mounting said baflle for movement between a first position obstructing the open end of said shield and a second position not obstructing the open end of said shield, means for moving said baflle into such first position, means for moving said baflie into such second position, a single pole, double throw enabling switch having a first position breaking the gas-cycle electrical control circuit and enabling the energizing of the oil-cycle electrical control circuit and a second position breaking the oil-cycle electrical control circuit and enabling the energizing of the gas-cycle electrical control circuit, means to retain said single pole, double throw switch in such first position except when said bafiie is in such first position, and means to retain said single pole double throw switch in such second position except when said bafile is in such second position.

5. In a furnace having a combustion chamber, at least one gas burner jet extending into the chamber for supplying gaseous fuel for combustion therein, gas control means for controlling the operation of the gas burner jet, an oil burner jet extending into the chamber for supplying oil fuel for combustion therein, and oil control means for controlling the operation of the oil burner jet, the improvement consisting in the combination of a shield surrounding the oil burner jet and having an open end extending into the chamber, a bafile for the end of said shield, means mounting said baffie for movement between a first position obstructing the open end of said shield and a second position not obstructing the open end of said shield, baffle moving means for moving said baffie into such first position and for moving said baffle into such second position, and baffle control means for selectively energizing the bafiie moving means to move the baffle alternatively to such first position or such second position, said gas control means being responsive to the position of said baflle to prevent firing of the gas burner jet when said baffle is in such second position, and such oil control means being responsive to the position of said baffie to prevent firing of the oil burner jet when said bafiie is in such first position.

6. In a furnace having a combustion chamber, at least one gas burner jet extending into the chamber for supplying gaseous fuel for combustion therein, a gas-cycle electrical control circuit for regulating the operation of the gas burner, an oil burner jet extending into the chamber for supplying oil fuel for combustion therein, and an oil cycle electrical control circuit for regulating the operation of the oil burner, the improvement consisting in the combination of a shield surrounding the oil burner jet having an open end extending into the chamber, a combustion air blower connected to the shield to deliver air therethrough to the chamber to support combustion of the oil fuel and subject to control of the oil-cycle electrical control circuit, a bafi'le for the end of said shield, means mounting said baffle for movement between a first position obstructing the open end of said shield and spaced therefrom to allow flow of air between said open end and said baffie under the influence of draft from the chamber and a second position not obstructing the open end of said shield, means for moving said baffle into such second position, gas switch means in the gas-cycle electrical control circuit having an open positon breaking such circuit and a closed position enabling the energizing of such circuit, oil switch means in the oil-cycle electrical control circuit having an open position breaking such circuit and a closed position enabling the energizing of such circuit, means to retain said gas switch means in the open position except when said baffle is in such first position, and means to retain said oil switch means in such open position except when said bafile is in such second position.

References Cited in the file of this patent UNITED STATES PATENTS 1,476,913 Nordensson et a1 Dec. 11, 1923 1,876,962 Klahn Sept. 13, 1932 2,542,684 Laverdisse et al Feb. 20, 1951 

